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Mag housing, to whack or not

Technical help for Series one, two and three Lambrettas. Models include the Li, Li Special, TV, SX, GP, Serveta and API/SIL models

Mag housing, to whack or not

Postby Tequipment » Sun Jul 12, 2020 8:27 pm

After eventually getting the piston and cylinder off, I've moved onto frustration number 2, the notorious mag housing.

Mine is totally stuck. I've repeatedly tried a lot of heat with a blow torch, I've wound the m6 bolts in as tight as I dare and I've tried standing the casing on its end in a drum of diesel for a week, but it won't budge at all and I'll break it if I hit it any harder.

I think I have 2 options, leave it in place, or try to knock the mag housing out with the crankshaft.

Is leaving it in place actually an option? The bearings either side of the crank seem tight and smooth and the seals don't leak, but the con rod has about 2mm of sideways movement if I hold it at the small end.
I'm getting contradicting advice on whether this is acceptable and can be centralised by shimming the small end.

Option 2 is ruin the crank and use it to knock the mag housing off.
I'd rather keep the crank if possible after all the effort saving it.
I've looked at how to knock it out and I'm probably missing something obvious, but I can't see how it can move sideways by hitting the drive side of the crankshaft.
the webs of the crank sit proud of the end of the casing, so hitting it will just move it a couple of millimeters until it hits the casing. See photo.
My big worry in all of this is damaging the casing.
Am I doing something wrong?

Image20200712_173244 by Dan Barrett, on Flickr
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Re: Mag housing, to whack or not

Postby Fast n Furious » Sun Jul 12, 2020 10:31 pm

The crank webs cant be bigger than the mag flange boss. If they were, the crank would never go in.
That crank looks knackered anyway, so using it to persuade the magflange off is a no brainer really.
Before giving the crank a whack with a heavy copper faced mallet, I would turn the crank to BDC, push the rod to one side and then brace the open web gap with a steel wedge driven in there to equalise the force across the face of the boss when it gets whacked. Sometimes the copper face mallet has been upgrade to a 4Lb lump hammer :o .
If yer aim with a hammer is a bit crap then I'd advise the use of a steel drift. (Ally casings don't like lump hammers)
Once you get it moving back and forth a little bit you should be able to remove the wedge and then tap it out the rest of the way, until the codrod gets in the way. At this point it should be possible to tap the crank back in and persude the magflange off.

Good luck.
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Re: Mag housing, to whack or not

Postby Tequipment » Sun Jul 12, 2020 10:47 pm

Thanks for the tips FnF.
What I meant was, I'll need to hit the crank to the left in the photo, but the shiny silver top of the web you can see is sitting higher than the blackened part of the engine casing to the left of it.
I tapped the drive side of the crankshaft, where the cush drive would go, and the whole crank moved across a couple of millimeters and then that shiny part of the web you can see, touched the black looking aluminium part of the casing.

Like I said, I'm probably being a complete tool, but if I start hitting the crankshaft, it looks like I'll just be whacking it into the casing. It's almost as if it needs to be lower down into the casing to work.
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Re: Mag housing, to whack or not

Postby Tequipment » Sun Jul 12, 2020 10:56 pm

Hang on! Is that blackened bit the back of the mag housing, and not part of the casing? :shock:
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Re: Mag housing, to whack or not

Postby Fast n Furious » Mon Jul 13, 2020 1:17 am

I think the penny has dropped. :lol: :lol: :lol: :oops:
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Re: Mag housing, to whack or not

Postby Warkton Tornado No.1 » Mon Jul 13, 2020 3:37 am

No doubt you'll need to resort to considerable force from the drive side, but if all retaining studs for the mag flange are removed, you can try making some kind of attachment that is secured to the two M6 extract holes, preferably by studs with nuts & washers.

The idea is then to try & obtain some angular movement via the attachment. If you can start to move the magneto housing with the increased purchase that the attachment should give you, even a nat's ACW then CW, then the 'seal' (due to decades of aluminium oxidation) will be broken & eventually allow the complete removal, Just don't be tempted to use the head cowling supports for rotational leverage as they will break.....
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Re: Mag housing, to whack or not

Postby Tequipment » Mon Jul 13, 2020 12:51 pm

:lol:
There doesn't look like there's a joint there at all, as its coated in 60 years worth of black varnish.

Are those 6mm studs, or the threads they're going into, strong enough to cope with twisting?
Are you tapping it to twist it, or just using as much force as possible?
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Re: Mag housing, to whack or not

Postby Fast n Furious » Tue Jul 14, 2020 12:17 am

The magflange is secured to the main casing via 3 x M6 studs, washers and nuts. It's very unlikely that you will be able to remove these studs prior to removal of the flange. Therefore, your ability to nudge the magflange rotationally to free off the electrolytic oxide is a non starter.
Best to just try moving it in and out to free it up. There are 2 x M6 threaded extraction holes at the 12 and 6 o'clock positions. Use 2 long setscrews here to assist with the extraction. Don't put too much torque on these threads as they will easily strip. Just tension them and then tap the crank end as suggested previously. Repeat until it's off.
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Re: Mag housing, to whack or not

Postby Warkton Tornado No.1 » Tue Jul 14, 2020 6:19 pm

Fast n Furious wrote:The magflange is secured to the main casing via 3 x M6 studs, washers and nuts. It's very unlikely that you will be able to remove these studs prior to removal of the flange. Therefore, your ability to nudge the magflange rotationally to free off the electrolytic oxide is a non starter.
Best to just try moving it in and out to free it up. There are 2 x M6 threaded extraction holes at the 12 and 6 o'clock positions. Use 2 long setscrews here to assist with the extraction. Don't put too much torque on these threads as they will easily strip. Just tension them and then tap the crank end as suggested previously. Repeat until it's off.


The method I described has worked for me, but I ensure that the M6 nuts used to lock on the studs are first class fully threaded to ensure removal. Perhaps I have been lucky, but I have never had to resort to forcing out via the crankshaft. I would do so as a last resort, though :)

Often the two extract holes are already dodgy in any case, but Helicoiling in situ is second nature as I have the kit.

In some instances I have applied some load via high tensile SHCS's via the extract holes & applied high, localised heat via oxy-acetylene to the main case to gain some movement, augmenting this with wedging between the mag flange gasket faces. However, my belief is that applying rotational force is constructive when assembling or dis-assembling mag flanges.
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Re: Mag housing, to whack or not

Postby Tequipment » Tue Jul 14, 2020 6:48 pm

Thanks for the tips guys. I take appreciate your time in replying.
The cylinder end of the case is currently sitting full of diesel, in the hope it'll help even a few percent.
The weekend is when I'll have a proper go at it.
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Re: Mag housing, to whack or not

Postby Tequipment » Fri Aug 07, 2020 10:59 am

I thought I'd better reply to give an update for people searching in the future.

It's out!

I changed my blowtorch from butane to butane/propane mix for a bit more heat and kept heating the engine casing and hammering the crank.
I also tapped out the M6 holes that were stripped to M8, and then when they stripped I went to M10. At this point I thought I was getting a lot of movement, but it turned out that it had cracked the mag flange.
I kept the bolts in to add a small amount of pull to assist my hammering, but the flange soon fell off.

The heating and hammering continued. After about 4 hours there was a 3mm gap. As I couldn't really see the gap increasing it felt like nothing was happening, but using feeler gauges and my vernier kept reassuring me I was actually making progress. I also scored a line on the mag flange in the gap, so I could see if it had moved.
Day 2 was another 4 hours, but this gave me another 5mm of movement. Day 3 was 10mm and as the contact area was reducing I started making better progress.
Then I got to the stage where the con rod needed holding central so that it didn't catch on the little triangular pieces in the cylinder hole. A sponge tucked in there was employed for this purpose after my other half looked like she had enough of being my con rod holder while I swung a club hammer and blow torch about.
Eventually it gave up it's 60 year hold.

A couple of things to keep in mind if someone else is in the same boat-
If it's really stuck, then the crankshaft will mushroom over, even when using a copper mallet. It's worth putting a bolt in the hole in the end of it and hitting that, otherwise it might not fit through the bearing. Luckily mine just fitted through as it was too mushroomed to get a bolt in by the time I thought of that. It'll also be useful if you're prepared to sacrifice a socket, as your drift won't slip off then.
Find some firm rubber about 10mm thick and cut it so that it fits in the casing. Cut a hole in it for the crank to poke through. This way, if you miss one of the thousand hits you'll be doing with your club hammer, you won't damage your engine casing. Don't forget to take it out every time you blowtorch it. ;)
Take your time. Although progress may be slow, it's better to be slow than get frustrated and damage the engine casing.

I then faced my next challenge. Those 4 screws holding in the bearing cover.
They looked like they were the originals and had no signs of ever having a screwdriver in them. They were centre punched to hold them in place.
I dug out my impact driver and found a good fitting flat headed screwdriver bit. I needed an extension bar to make sure he impact driver was clear of the casing and so it could be held perfectly straight.
I used a pick to make sure the screw heads were completely clear of crud so the bit had the best chance of gripping.
One good tap while twisting and the first screw came out. This was followed by the other 3. It couldn't have been easier!
Maybe all the heat and weeks in diesel had actually done some good.

Now everything is cleaned I can start rebuilding with new bits. What could possibly go wrong with that. :roll:

Thanks to all who contributed with advice above. I couldn't have done it without you.
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Re: Mag housing, to whack or not

Postby Toddy » Fri Aug 07, 2020 1:16 pm

Thanks for the update it’s always a great feeling when it comes off after all the hard work :D
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Re: Mag housing, to whack or not

Postby Fast n Furious » Fri Aug 07, 2020 4:32 pm

Well done.
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Re: Mag housing, to whack or not

Postby dickie » Fri Aug 07, 2020 10:53 pm

Victory at last. The sweet taste of success.

Another tip from a similar one I did last year. After it had shifted 2 or 3mm, I hammered the mag flange back in. Knocked it in and out a good few times, but I think it made it easier than just one direction.

I did however, crack the mag flange doing this. :lol:
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Re: Mag housing, to whack or not

Postby hullygully » Mon Aug 10, 2020 4:27 pm

well done too , we all luv a happy ending
I think Broady used to do a mag flange puller..........
plus you can use those M6 tee bars, but you having to resort to M10 bolts!!!!!!!! geez that was a tight one :shock:
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Re: Mag housing, to whack or not

Postby Jeff t » Tue Oct 13, 2020 12:40 pm

Just going through the same problem, even cut the con rod off to make sure I don’t damage the casing. Mag Flange has moved and it’s about 13mm out but seems to have locked up again, just checking should hitting the crank get it all the way out only sounds like it’s bottomed out
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Re: Mag housing, to whack or not

Postby dickie » Wed Oct 14, 2020 9:22 am

Jeff t wrote:Just going through the same problem, even cut the con rod off to make sure I don’t damage the casing. Mag Flange has moved and it’s about 13mm out but seems to have locked up again, just checking should hitting the crank get it all the way out only sounds like it’s bottomed out

I had a real bad one a year or two ago which did this. I ended up knocking it back in and out a few times to be able to completely remove it. This was a mistake as it caused it to crack. If I were to do it again, I'd just persevere with whacking the crank. It will go. Or break you.... :lol:
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Re: Mag housing, to whack or not

Postby Jeff t » Wed Oct 14, 2020 7:50 pm

It’s out, bit more persuasion round the edge with a mallet and piece of wood :D :D
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